(1) Field of the Invention
The present invention relates to an apparatus for controlling the winding speed of roving in a so-called bobbin-lead type roving frame, wherein a roving twisted by a flyer rotated at a predetermined speed is wound on a bobbin rotated at a speed higher than the rotation speed of the flyer to form a package of a predetermined size. More particularly, it relates to an apparatus for controlling the winding speed of the roving in the above-mentioned roving frame wherein the winding speed of the roving is automatically controlled so that the tension on the roving is always maintained at a desired value during the period from the starting point of the winding operation to the point of the completion of forming a full-package roving bobbin.
(2) Description of the Prior Art
In winding a twisted roving in the form of layers on a bobbin in a conventional bobbin-lead type roving frame, in order to always maintain the winding speed of the roving at the same level as the spinning speed of the roving from a drafting apparatus, a mechanism for reducing the winding speed, including a pair of cone drums, is built in a bobbin driving system, and an endless belt wound mounted on the paired cone drums is displaced by a predetermined distance for forming every layer of a package so that the rotation speed of the bobbin can be gradually decreased from one layer to the next layer of roving.
However, the winding speed of the roving for every layer is not simply proportional to the number of layers of the roving but is delicately changed according to the spinning conditions such as the kind of roving fiber, the properties of the fiber, the count number of the roving, the twist number of the roving, and the compressive force of a presser. Accordingly, where only one kind of paired cone drums is used in which the design is based on a certain special spinning condition, it is practically very difficult to maintain the winding speed of the roving for every layer of the package at the same level throughout a broad range of the spinning conditions. Therefore, a system in which the displacement distance of the belt for forming every layer of a package is adjusted by an auxiliary cam that can be adjusted according to the spinning conditions has been marketed. However, the method using this auxiliary cam is not preferred from the practical viewpoint because trial spinning should be effected to determine the displacement distance of the belt along the cone drums for forming every layer of a package, every time the spinning conditions are changed.
Recently, Japanese Examined Patent Publication No. 51-22532 has proposed a method in which the number of teeth of a ratchet wheel, which is a driving source of a shifter for displacing a belt along paired cone drums, is set at a level smaller by about one than a predetermined tooth number so that the belt is slightly over-displaced and a roving being wound between the nip point of the front roller of a drafting device and a flyer is slackened. The accumulation of such slack is detected by photoelectric means to actuate a control motor for only a short time and this control input is applied to a gear row from a gear engaged with a rack lever of the shifter to the ratchet wheel to slightly return the forward displacement of the belt, whereby the rotation speed of the bobbin is corrected. According to this method, at every exchange of the yarn layers on the bobbin, the belt is over-displaced and the roving is wound under the slightly slackened condition, and when such slacks of roving, which are created between the nip point of the front rollers of the drafting device and a flyer, are accumulated, the position of the belt is returned to increase the roving tension and the roving is wound in this state. Accordingly, when a roving is wound according to this method, the roving tension is increased once for a certain number of layers, and the adjusted value of roving tension changed by one correction is relatively large, so that there is a strong possibility of an abrupt change in the roving tension. Therefore, deformation is readily caused on both ends of the package. Moreover, when the count number of the roving which is related to the winding speed, is changed beyond a certain degree, the tooth number of the ratchet wheel should be changed.
Furthermore, Japanese Examined Patent Publication No. 56-25525 proposes a roving winding apparatus in a roving frame, in which an external force is applied to a roving between a front roller of a drafting device and a flyer top by a jetted air stream to positively vibrate the roving, the inherent frequency of vibration being measured by a frequency measuring device. The inherent frequency of vibration is compared with a predetermined frequency, and when there is a deviation of the inherent frequency of vibration from the predetermined frequency of vibration, the rotation speed of the bobbin is increased or decreased according to the value of this deviation so that the roving is wound under a constant roving tension throughout the period from the start of the winding operation to the completion of the winding operation. However, in this roving winding apparatus, an air stream is intermittently jetted against the roving between the front roller of the drafting device and the flyer top to positively create the vibration of the roving, and the pressure of the air stream intermittently jetted against the roving acts on a sample spindle provided with an air jetting device. Therefore, especially in the case of a loosely twisted roving of a synthetic fiber or a blend thereof, irregular drafting is readily caused in the roving between the front roller and the flyer top and many fluffs are possibly created. Moreover, a difference in the roving tension is created between the sample spindle and other spindles, because of the jetting of an air stream onto the roving of the sample spindle. Accordingly, this apparatus has a defect such that it is impossible to maintain uniform winding conditions in all the spindles. In this roving winding apparatus, an external force is applied to a roving between the front roller and the flyer top to positively create the vibration of the roving, the inherent frequency of vibration at the time of application of this external force being measured as a value corresponding to the roving tension. This inherent frequency of vibration is compared with a predetermined frequency of vibration, and the rotation speed of the bobbin is increased or decreased according to a deviation of the inherent frequency of vibration from the predetermined frequency of vibration. Accordingly, in this roving winding apparatus, the value of the frequency of vibration predetermined by a preset value defining device is an important factor for maintaining the roving tension at a certain appropriate level. The frequency of vibration varies according to the differences of the count number of the roving and the kinds of fibers concerned. Accordingly, in order to regulate the predetermined frequency of vibration to an appropriate value within a broad range of spinning conditions (such as the kinds and properties of the fiber, the count number of the roving, and twist number of the roving), it is necessary to find an appropriate roving tension for respective spinning conditions by trial spinning, and to determine the inherent frequency of vibration at the time when a jet air stream blows against a roving under the appropriate roving tension and to set the so-determined inherent frequency of vibration in the preset value defining apparatus. Accordingly, in such a conventional roving frame provided with a roving winding apparatus as mentioned above, even if the roving winding apparatus has a function of winding a roving under a constant roving tension, in order to determine the predetermined frequency of vibration in the winding apparatus, the above-mentioned troublesome operations, which are more complicated than the operations adopted in the conventional roving frame provided with the auxiliary cam, should be performed every time the spinning conditions are changed. Thus, the roving frame of this type is not preferred from the practical viewpoint.
It is well known that a centrifugal force imposed on a roving which forms the outside layer of a bobbin is increased as the diameter of the bobbin is increased. Such increase of the centrifugal force is distinguished if the rotation speed of the flyer is increased. Because of the recent tendency of increasing the speed of the roving frame, it must be recognized that the increase of the speed of the roving frame produces an undesirable increase of such centrifugal force by which weak portions of roving are frequently created, so that the number of breakages of the roving is increased as compared with the conventional roving frame. This has become a serious problem which must be solved. Accordingly, there has been adopted a method in which the rotation speed of the machine is gradually decreased with the increase of the wound diameter of the bobbin. This method, however, is defective in that since the rotation speed of the machine per se is decreased, the production rate is decreased. If it is intended to increase the production rate by increasing the operation speed, this method is not suitable and the apparatus becomes complicated and expensive.
Incidentally, it is known that in the spinning operation in a roving frame, uneven twisting is caused while a roving is fed from a front roller and wound on a bobbin, and a loosely twisted portion is poor in tensile strength and the strength of this portion is further reduced by a tension or frictional force imposed on the roving during the spinning portion. This portion will be called the "weak portion of the roving" hereinafter.